WO2009004348A2

WO2009004348A2 - Slump retention-enhanced cement dispersants

Info

Publication number: WO2009004348A2
Application number: PCT/GB2008/002299
Authority: WO
Inventors: David William Hughes; Ernie Norris
Original assignee: W.R. Grace & Co. - Conn
Priority date: 2007-07-02
Filing date: 2008-07-02
Publication date: 2009-01-08
Also published as: WO2009004348A3; GB0712806D0

Abstract

The present invention provides a composition and method involving the use of at least one cement dispersant mixed with a diphosphonic or triphosphonic acid or salt as a slump retention-enhancing agent that is chemically unreacted with the at least one cement dispersant, such that, when introduced into the aqueous environment of a cementitious mixture, slump retention-enhancing agent molecules move independently of cement dispersant molecules with respect to the cement particles.

Description

SLUMP RETENTION-ENHANCED CEMENT DISPERSANTS

Field of the Invention

The present invention relates to cement dispersants for hydratable cementitious compositions such as concrete and mortar. More particularly, the present invention relates to combinations and methods wherein a cement dispersant is mixed with, but not chemically reacted with, a slump retention- enhancing additive comprising a diphosphonic or triphosphonic acid or salt thereof. Background of the Invention

Cement dispersants have been used in the construction industry to disperse (e.g., to fluidify or to plasticize) hydratable cementitious mixtures such as mortar, which contains a cement binder and a fine aggregate such as sand, or such as concrete, which further contains a coarse aggregate such as crushed stone. Such cement dispersants improve the flow characteristics of the cementitious slurry by breaking up cement agglomerates and freeing the water, thereby providing slurries having relatively lower viscosity and permitting desirable flow conditions to be obtained at lower pump pressures.

Conventional cement dispersants contemplated for use in the present invention include sulphonated melamine formaldehyde condensate and sulphonated naphthalene formaldehyde condensate, all of which are considered as low- or mid- range water reducers because they replace approximately 5% to 12% of the water otherwise required for fluidifying and hydrating the cement mixture. Conventional dispersants also include "superplasticizers," which are dispersants that replace 15% or more of the water otherwise required; and these specifically include polycarboxylate

("PC") polymeric dispersants copolymerized from acrylate or methacrylate monomers (e.g., polyalkylene glycol(meth)acrylate) and carboxylic acid monomers, and optionally other monomers which are copolymerized with such monomers. Some of these PC dispersants have "comb" structures comprising a backbone and pendant carboxylic and/or polyoxyalkylene moieties that provide the molecules with cement-dispersing capabilities. Such PC cement dispersants surround the cement particles, while repulsion forces between the polymer chains work to repel the particles apart from each other, and thus render the cementitous mixture more fluid.

The present inventors seek to fulfill several objectives simultaneously through the use of the invention. One objective is to enhance slump retention such that the cementitious mixture can remain workable over a longer period of time. The term "slump" refers to fluidity as measured using a standard "slump" cone, whereby a cementitous mixture is placed into a cone that is is inverted onto a table surface and removed from the mixture, so that the slump or sag of the cementitious sample can be measured as a function of time.

Another objective is to resist segregation of the aggregates, or, in other words, to achieve fluidity of the cementitious mixture without increasing the risk that the aggregates will precipitate out of the mixture and cause "bleeding" or separation of the water portion from the mixture.

A further objective, one that is of equal importance to the first objective described above, is to avoid loss of early strength. Early strength refers to the compressive strength of the hardening cementitious mixture within the first 24 hours after water is mixed with the cement binder to initiate curing.

A still further objective is to provide dispersing characteristics that remain "robust" despite varying levels of C₃A (tricalcium aluminate), alkaline content, and sulphate in the cement binder.

An early approach to extending the workability period of the cement mixture having a dispersant was to incorporate a set retarder, such as sodium gluconate. However, this resulted in a loss of early strength, as well as a substantial alteration of the setting characteristic of the mixture.

In view of the foregoing discussion, a novel composition and process are needed. Summary of the Invention

In surmounting the disadvantages of the prior art, the present invention provides a composition and method, wherein a slump retention-enhancing agent is combined with a cement dispersant, to extend the slump life of a hydratable cementitious mixture, such as fresh concrete or mortar, without decreasing early compressive strength.

An exemplary cement dispersant composition of the invention comprises (A) at least one cement dispersant comprising (i) sulphonated melamine formaldehyde condensate; (ii) sulphonated naphthalene formaldehyde condensate; or (iii) copolymers formed by polymerizing an acrylic or methacrylic monomer, a carboxylic acid monomer, and optionally a further monomer or monomers copolymerizable with the foregoing monomers; and (B) a slump retention-enhancing agent comprising a diphosphonic or triphosphonic acid or salt thereof, which is chemically unreacted with the at least one cement dispersant, such that, when the cement dispersant composition is mixed with a hydratable cementitious composition, the molecules of the cement dispersant and slump retention-enhancing agent can move independently of the other with respect to cement particles. The slump retention of the hydratable cementitious mixture is extended when compared to a cementitious mixture containing only the cement dispersant.

Thus, an aspect of the invention relates to a cement dispersing composition comprising (A) at least one cement dispersant comprising (i) sulphonated melamine formaldehyde condensate; (ii) sulphonated naphthalene formaldehyde condensate; or (iii) copolymers formed by polymerizing an acrylic or methacrylic monomer, a carboxylic acid monomer, and optional further monomer or monomers copolymerizable with the foregoing monomers; and (B) a slump retention-enhancing agent selected from a diphosphonic acid, trisphosphonic acid, or salt thereof, wherein said slump retention-enhancing agent is chemically unreacted with said at least one cement dispersant, such that, when said cement dispersing composition is mixed with a hydratable cementitious mixture, said slump retention- enhancing agent molecules can move independently of the cement dispersant molecules with respect to the cement particles.

An exemplary slump retention-enhancing agent has a structure represented by the formula G[PO₃Ha]_n wherein G represents a bridging group that operates to bridge two or three phosphonic acid or salt groups (PO3H2), and n is 2 or 3 (n represents the number of phosphonic acid or salt groups attached to said G bridging group). The bridging group "G" may comprise a substituted or unsubstituted alkyl group (preferably a substituted or unsubstituted Ci to C₄ alkyl group); an amine (preferably a secondary or tertiary amine); a carboxyl; a sulfate; a sulphonate; an ether; an aldehyde; a ketone; a thiol; or an oxyalkylene group.

It is preferred that in said slump retention-enhancing agent, n = 2 and said slump retention-enhancing agent has a structure represented by

OH OH \ /

O = P - G - P = O / \

OH OH.

For example, a preferred diphosphonate slump retention-enhancing agent having an alkyl "G" group should ideally have no more than four carbon atoms bridging (and spacing apart) the phosphonate groups, but more preferably only one carbon atom would be used to bridge the phosphonate groups (as in methyl-diphosphonic acid or as in 1-hydroxyethane-1 ,1- diphosphonic acid). It is preferred that the slump retention-enhancing agent is a diphosphonic acid or a salt thereof wherein said bridging group G is a substituted or unsubstituted alkyl group.

Preferred slump retention-enhancing agents include methane- diphosphonic acid/salt, hydroxyethane-diphosphonic acid/salt (preferably 1- hydroxyethane-1 ,1 -diphosphonic acid or a salt thereof), and nitrilotris(methylenephosphonic) acid/salt thereof. Most preferred slump retention-enhancing agents have small bridging groups "G" wherein no more than one carbon, nitrogen, oxygen, or sulfur group separates two phosphonate groups (-PO₃H₂) from each other. Even more preferred is a diphosphonic acid having no more than one carbon atom intervening between phosphonate groups.

In exemplary slump retention-enhancing agents, the bridging group

"G" may be a substituted Ci to C₄ alkyl group, and in such case the substituent groups may be selected from an alkyl group, an aromatic group, an alcohol, a halogen, an amine, an aldehyde, a ketone, carboxyl, sulfate, carbonyl, oxyalkylene, or mixture thereof.

Preferably, in the cement dispersing compositions of the invention, said at least one cement dispersant is present in the amount of 2% - 50%, and wherein said slump retention-enhancing agent is present in the amount of

0.3% - 10%, all percentages herein are dry weight based on total weight of said cement dispersing composition.

In an exemplary cement dispersing composition of the invention, said at least one cement dispersant comprises said copolymers, said copolymers comprising polyacrylate comb polymers.

In another example of a cement dispersing composition of the invention, said at least one cement dispersant comprises sulphonated naphthalene or melamine formaldehyde condensate.

The cement dispersing compositions of the invention may further comprise a lignosulfonic acid or salt as an additional cement dispersant.

Another aspect of the invention relates to a cement composition comprising a cement binder and the cement dispersing composition of the invention. Thus, the invention also relates to a cementitious composition comprising a (A) cement binder; (B) least one cement dispersant comprising

(i) sulphonated melamine formaldehyde condensate; (ii) sulphonated naphthalene formaldehyde condensate; or (iii) copolymers formed by polymerizing acrylic or methacrylic monomer, a carboxylic acid monomer, and optional further monomer or monomers copolymerizable with the foregoing monomers; and (C) a slump retention-enhancing agent selected from a diphosphonic or triphosphonic acid or salt thereof, wherein said slump retention-enhancing agent is chemically unreacted with said at least one cement dispersant, such that, when said cement dispersing composition is mixed with a hydratable cementitious mixture, slump retention-enhancing agent molecules can move independently of cement dispersant molecules with respect to the cement particles.

The present invention also provides methods of modifying hydratable cementitious mixtures by mixing cement with the above-described cement dispersant and diphosphonic or triphosphonic acid/salt slump retention- enhancing agent. Again, the slump retention-enhancing agents are chemically unreacted with the cement dispersant, and therefore operative to move independently from the cement dispersant molecules within the aqueous environment of a hydratable cement mixture. The invention also contemplates cement compositions made by incorporation of the foregoing dispersant and agent.

Further advantages and features of the invention are described in detail hereinafter.

Detailed Description of Exemplary Embodiments The present invention provides a composition and process for modifying the rheology, and especially for enhancing slump retention, of a hydratable cementitious mixture.

The cement dispersant and phosphonic acid or salt components may be alternatively referred to in their salt or acid forms, but the use of one term herein (e.g., diphosphonic acid) will also include its salt form (diphosphonate) and vice-versa. In other words, the use of the terms disphosphonate or lignosulphonate, for example, will also be include their corresponding acid forms (e.g., diphosphonic acid, lignosulfonic acid).

The term "cementitious mixture" refers to pastes, mortars, and concrete compositions comprising a hydraulic cement binder which, when combined with water and mixed, will initiate a curing reaction resulting in the hardening of the cementitious mixture. Pastes are defined as mixtures composed of a hydraulic cement binder, either alone or in combination with pozzolans, such as fly ash, silica fume, or granulated blast furnace slag, and water. Mortars are defined as pastes that additionally include fine aggregate such as sand. Concretes additionally include coarse aggregate such as crushed gravel or stones. These compositions may additionally include other admixtures, such as set retarders, set accelerators, defoaming agents, air-entraining or air detraining agents, corrosion inhibitors, water reducing agents, pigments, shrinkage reducing agents, and/or any other admixture that does not adversely affect the advantageous results obtained by the present invention. These other admixtures may be added directly into the cementitious mixture, or introduced as an additional component to the cement dispersing compositions herein described.

As summarized above, an exemplary cement dispersant composition of the invention comprises (A) at least one cement dispersant comprising (i) sulphonated melamine formaldehyde condensate; (ii) sulphonated naphthalene formaldehyde condensate; or (iii) copolymers formed by polymerizing an acrylic or methacrylic monomer (such as polyalkylene glycol(meth)acrylate), a carboxylic acid monomer, and optional further monomer copolymerizable with the foregoing monomers; and (B) a slump retention-enhancing agent comprising a diphosphonic or triphosphonic acid or salt thereof, which is chemically unreacted with the at least one cement dispersant, such that, when the cement dispersant composition is mixed with a hydratable cementitious composition, the molecules of the cement dispersant and slump retention-enhancing agent can move independently of the other with respect to cement particles.

It is contemplated that conventional sulphonated melamine formaldehyde condensate (MSFC) or sulphonated naphthalene formaldehyde condensate compounds (NSFC) can be employed as suitable cement dispersants in the present invention. In further exemplary embodiments, MSFC or NSFC can be supplemented with a secondary cement dispersant such as a lignosulfonate (e.g., calcium or sodium lignosulfonic acid or salt). Alternatively, certain polycarboxylate or PC polymers can be employed as suitable cement dispersant in the invention. The term "polycarboxylate" (or "PC") as used herein shall be interpreted to mean and refer to copolymers formed by polymerizing an acrylic or methacrylic monomer (e.g., polyalkylene glycol(meth)acrylate), a carboxylic acid monomer, and optionally a further monomer or monomers copolymerizable with the foregoing monomers, as known to those of ordinary skill in the art. For example, US Patent No. 5,925,184 and 6,087,418, both owned by Nippon Shokubai Co., Ltd., disclosed such PC polymers which are deemed suitable for use in the present invention. The term "polyalkylene glyco!(meth)acryiate" as used herein is intended to include acrylate as well as methacrylate monomers.

For example, such suitable conventional polycarboxylate polymers are polycarboxylated polyethers having comb polymer structures with backbone carboxyl groups that function to attach to the cement particles, and groups pendant to the backbone and containing polyoxyalkylene groups that function to disperse the cement particles.

Polycarboxylate polymers suitable for use in the invention are commercially available from Grace Construction Products under the trade name "ADVA®." These imidized polyacrylic acid polymers or copolymers are disclosed in US Patent No. 5,393,343. Polyoxyalkylene amines are grafted onto a polycarboxylic acid backbone in an amidization/imidization reaction. These polymers are sold in the form of a metallic salt made by final reaction of the polymers with a base, such as sodium or calcium hydroxide.

Many other polycarboxylate polymers are also commercially available and believed suitable for use in the invention, including those commercially available from BASF under the trade name MELFLUX® and SOKOLAN®, from KAO Corporation under the trade name MIGHTY®; from Nippon Shokubai under the trade name AQUALOC®; from LYONDELL under the trade name ETHACRYL®. The present invention specifically excludes polycarboxylate polymer cement dispersants made from maleic anhydride and/or allyl ethers. It is believed that such polymers, although containing polycarboxylic acid groups operative to disperse cement particles, have certain disadvantages such as setting issues due to extended retardation, and these do not act sufficiently quickly for achieving early fluidity of the cement mix.

Exemplary slump retention-enhancing agents of the present invention have a structure represented by the formula G[PO₃H₂]_n wherein G represents a bridging group that operates to bridge two or three phosphonic (PO₃H₂) acid or salt groups and which is itself not a phosphonic acid or salt group, and n is

2 or 3 and represents the number of phosphonic acid or salt groups attached to the G bridging group. Exemplary bridging groups "G" may comprise a Ci to C₄ substituted or unsubstituted alkyl group, a secondary or tertiary amine, a carboxyl, a sulfate, a sulphonate, an ether, an aldehyde, a ketone, a thiol, or an oxyalkylene group.

Hence, the slump retention-enhancing agent may have a disphosphonate (OH)₂OP — G¹ — PO(OH)₂ structure which is represented as OH OH

\ /

O = P - G¹ — P = O Formula (1)

/ \

OH OH

or, the slump retention-enhancing agent may have a triphosphonate [POsH₂J₃ structure which is represented as

PO(OH)₂ / (OH)₂OP - G² Formula (2)

\ PO(OH)₂

Consequently, in the diphosphonate structure shown above (Formula (1)), G¹ could be an substituted or unsubstituted Ci to C₄ alkyl group (such as a methyl group in methane-diphosphonic acid/salt or such as the substituted ethane group in 1-hydroxyethane-1 ,1-diphosphonic acid). As another example, in the trisphosphonate structure shown above (Formula (2)), G² could be a tertiary amine, such as with a nitrogen group having three methyl groups, such as in nitrilotris(methylenephosphonic acid). The nitrolotris(methylenephosphonic) acid group may be represented as follows:

CH₂ — PO(OH)₂ / (OH)₂OP — CH₂ — N

\ CH₂ — PO(OH)₂

While it has been mentioned that the bridging group "G" (as shown in Formula 1 and 2 above) may comprise a Ci to C₄ substituted or unsubstituted alkyl group, a secondary or tertiary amine, a carboxyl, a sulfate, a sulphonate, an ether, an aldehyde, a ketone, a thiol, or an oxyalkylene group, it is preferred that as few molecules as possible be used for connecting (and hence spacing apart) the two or more phosphonate groups.

In exemplary embodiments, the at least one cement dispersant and phosphonate-based slump retention-enhancing agent can be provided in the form of a premixed admixture composition that can be admixed into the hydratable cementitious mixture; or the components may be added separately, although this latter method is much less convenient.

The slump retention-enhancing agent may be incorporated into the manufacturing process whereby cement is manufactured from ground clinker, or the cement dispersant can be added either during such cement manufacture operation, or added later when aggregate is combined with the cement to form a mortar or concrete mixture. For example, a secondary amine diphosphonate or a tertiary amine triphosphonate such as nitrilotrisfmethylenephosphonic acid] may have benefits as cement grinding aids which can be combined with cement clinker either before or during the grinding of such clinker to produce cement. When the cement dispersant and slump retention-enhancing agent are premixed together and provided to concrete producers (e.g., for use in ready- mix concrete, precast concrete, etc.), the preferred amounts of the components are as follows. A cement dispersing composition may contain at least one cement dispersant present in the amount of 2% - 50% (and more preferably 10% - 30%), and a slump retention-enhancing agent present in the amount of 0.3% - 10% (and more preferably 1.0% - 5.0%), all percentages reflecting the dry weight of the components based on total weight of cement dispersing composition. Preferably, the cement dispersing composition is provided as a liquid that may be conveniently pumped and metered into a concrete batch, such as typically would occur in a ready-mix plant or within the mixing truck.

In further exemplary methods of the invention, wherein the cement dispersant and slump retention-enhancing agent are mixed with cement binder, the preferred ranges of the components are as follows. The cement dispersants can be used in the amount of 0.02-0.50% (and more preferably 0.05-0.25%) actives and the slump retention-enhancing agent can be used in the amount of 0.003-0.100% (and more preferably 0.010 - 0.050%) actives, all percentages expressed in terms of dry weight based on dry weight of the cementitious binder. As previously mentioned, cement dispersing compositions of the invention may optionally include one or more conventional admixtures, such as set retarders, set accelerators, defoaming agents, air-entraining or air detraining agents, corrosion inhibitors, water reducing agents, pigments, shrinkage reducing agents, and the like, in amounts that are known to those of ordinary skill in the art.

In addition to mixtures of cement dispersants and slump retention- enhancing agents as above-described, the present invention also relates to cementtitious compositions and methods for modifying cementitious compositions using these components. Hence, an exemplary cementitious composition comprise a cement binder; at least one cement dispersant selected from the group consisting of sulphonated melamine formaldehyde condensate, sulphonated naphthalene formaldehyde condensate, and polycarboxylate polymer; and a slump retention-enhancing agent selected from a diphosphonic or trisphosphonic acid, or salt thereof, wherein the slump retention-enhancing agent is chemically unreacted with said at least one cement dispersant, such that, when said cement dispersing composition is mixed with a hydratable cementitious mixture, said slump retention-enhancing agent molecules can move independently of the cement dispersant molecules with respect to the cement particles.

Similarly, an exemplary method of the invention for enhancing slump retention in a cementitious mixture, comprises mixing together the cement binder, cement dispersant, and slump retention-enhancing agent as aforesaid.

While the invention is described herein using a limited number of embodiments, these specific embodiments are not intended to limit the scope of the invention as otherwise described and claimed herein. Modification and variations from the described embodiments exist. More specifically, the following examples are given as specific illustrations of embodiments of the claimed invention. The invention is not limited to the specific details set forth in the examples. All parts and percentages in the examples, as well as in the remainder of the specification, are by weight unless otherwise specified.

Further, any range of numbers recited in the specification or claims, such as that representing a particular set of properties, units of measure, conditions, physical states or percentages, is intended to literally incorporate expressly herein by reference or otherwise, any number falling within such range, including any subset of numbers within any range so recited. For example, whenever a numerical range with a lower limit, RL, and an upper limit RU, is disclosed, any number R falling within the range is specifically disclosed. In particular, the following numbers R within the range are specifically disclosed: R = RL + k^*(RU -RL), where k is a variable ranging from 1% to 100% with a 1% increment, e.g., k is 1 %, 2%, 3%, 4%, 5%. ...50%, 51 %, 52%, ...95%, 96%, 97%, 98%, 99%, or 100%. Moreover, any numerical range represented by any two values of R, as calculated above, is also specifically disclosed.

The following examples are provided for the purposes of illustration only, and are not intended to limit the scope of the invention.

Example 1

The dispersing properties of several conventional polycarboxylate (PC) cement dispersants and blends of PC dispersants were tested using various known cement hydration retarding admixtures and phosphorous-based compounds.

A control concrete mixture was prepared using on a commercially available polycarboxylate (PC) polymer cement dispersing composition, PC1 , which contained a defoamer. The amount of polymer was about 20% dry weight based on total liquid weight of the composition.

A series of comparative cement dispersing compositions were formulated using a combination of the PC1 cement dispersant and various phosphorous group-containing compositions, described as follows.

Sodium hexametaphosphate (SHMP) was dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and the SHMP present in the amount of 5% actives by weight of solution. Dihydrogen orthophoshate (DHOP) was dissolved and mixed with the

PC to obtain a second aqueous composition wherein the PC was present in the amount of 20% and the DHOP present in the amount of 5% by weight of solution.

Finally, 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with the PC to obtain a second aqueous composition wherein the PC was present in the amount of 20% and the 1-hydroxyethane- 1 ,1-diphosphonic acid present in the amount of 3% by weight of solution.

Concrete mixes, comprising a Portland cement, OPC-A, known to exhibit rapid loss of workability along with coarse and fine aggregates in proportions typical of a ready-mixed concrete mix design containing 350 kg/m³ cement, were prepared containing each of the four aqueous compositions described above. The workability of the four concrete mixtures was tested using a standard ASTM C 143 slump cone test at intervals of 30 minutes over a period of one hour or until the concrete reached an unusable consistency. The data results are summarized in Table 1 below. Table 1

*Solution weight by weight of cement.

The PC1 -HEDPA blend was found to significantly extend the time of workability (referred to as "slump life") compared to that of the other additives without causing any delay in strength gain of the concrete.

Example 2

The dispersing properties of a conventional polycarboxylate (PC1) cement dispersant were tested and compared with formulations containing a known retarder, sodium gluconate (SG), and 1-hydroxyethane-1 ,1- diphosphonic acid (HEDPA) A control concrete mixture was prepared using on a commercially available polycarboxylate (PC1) polymer cement dispersing composition, PC1 , which contained a defoamer. The amount of polymer was about 20% dry weight based on total liquid weight of the composition.

Sodium gluconate (SG) was dissolved and mixed with the PC1 to obtain a second aqueous composition wherein the PC1 was present in the amount of 20% and the phosphate present in the amount of 3%.

Sodium gluconate (SG) and 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) were dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and both the Sodium gluconate (SG) and 1-hydroxyethane~1 ,1-diphosphonic acid (HEDPA) were present in the amount of 1.5% each. Finally, 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and the 1-hydroxyethane-1 ,1- diphosphonic acid present in the amount of 3%.

Concrete mixes, made by combining OPC-A and coarse and fine aggregates in ' proportions typical of a self-leveling high flow Ready-mixed concrete mixture and containing 430 kg/m³ cement, were then prepared containing with one of the four aqueous compositions described above. The workability of each of the four concrete samples was tested using a standard slump-flow cone test at intervals of 30 minutes over a period of one hour or until the concrete reached an unusable consistency.

The data results are summarized in Table 2 below.

Table 2

^* Based on the ease of movement upon and cohesive non-segregating behaviour of the concrete .

No loss in workability is evident with the PC1 -HEDPA blend as compared to the performance of PC1-SG. SG is known for extending slump life by delaying cement hydration.

Example 3

The dispersing properties of a conventional polycarboxylate (PC) cement dispersant were tested and compared with formulations containing a known retarder, sodium gluconate (SG), and the 1-hydroxyethane-1 ,1- diphosphonic acid (HEDPA)

Sodium gluconate (SG) was dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and the phosphate present in the amount of 3%. Sodium gluconate (SG) and 1-hydroxyethane-1 ,1-diphosphonic acid

(HEDPA) were dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and both the sodium gluconate (SG) and 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) were present in the amount of 1.5% each. Finally, 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with PC1 to obtain a second aqueous composition wherein PC1 was present in the amount of 20% and the 1-hydroxyethane-1 ,1- diphosphonic acid present in the amount of 3%.

Mortar mixes, made by combining OPC-A and an EN 196 standard sand in the same proportions as found in a Ready-mixed concrete mix having an equivalent cement content of 350 kg/m³, were then prepared containing each of the four aqueous compositions described above. The workability of each of the four mortar samples was tested using a Mini Slump Cone (MSC) having dimension of XXX and Volume of YYY at intervals of 20 minutes over a period of two hours or until the mortar reached an unusable consistency. The data results are summarized in Table 3 below. Table 3

The workability of mortar mixture admixed with the PC 1 -HEDPA blend was extended to 100 minutes compared to the other mortar mixtures.

Example 4

The dispersing properties of a conventional polycarboxylate, PC1 , cement dispersant were tested and compared with a formulation containing 1- hydroxyethane-1 ,1-diphosphonic acid (HEDPA) in OPC-A and a second cement, OPC-B, known to be the cause of rapid loss of workability when used in concrete mixtures.

Secondly, 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with the PC to obtain a second aqueous composition wherein the PC was present in the amount of 20% and the 1-hydroxyethane- 1 ,1-diphosphonic acid present in the amount of 3%. Mortar mixes, made by combining OPC-A and OPC-B each with EN

196 standard sand in the same proportions as a typical high quality Ready- mixed concrete mix design having an equivalent cement content of 350 kg/m³, were prepared containing each of the aqueous compositions described above. The workability of each of the four mortar samples was tested using a Mini Slump Cone (MSC) having dimension of XXX and volume of YYY at intervals of 20 minutes over a period of one hour or until the mortar reached an unusable consistency. The retention of flow at each test time was then compared with the original flow value.

Table 4

The data results, summarized in Table 4, indicate how the slump extension, up to 68 to 80% after 1 hour, provided by the PC1 -HEDPA blends can apply to a number of cements that exhibit complete loss of slump by 40 minutes when admixed with just the PC1 cement dispersant.

Example 5

The dispersing properties of a blend of two conventional polycarboxylate cement dispersants, PC1 and PC2, were tested and compared with formulations containing a known retarder, sodium gluconate (SG), and various phosphorous-containing slump retention agents in a highly flowable concrete mixture design. The control admixture system was based on a blend of PC1 , PC2, and SG and a defoamer. The total amount of PC polymer was 37%, and the amount of SG was 6% by weight of solution.

Sodium tripolyphosphate (STPP) was dissolved and mixed with the PC1/PC2 blend to obtain a second aqueous composition wherein the PC blend was present in the amount of 37% and the sodium tripolyphosphate (STPP) was present in the amount of 6%.

1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with the same PC composition as above to obtain a third aqueous composition wherein the PC was present in the amount of 37% and the 1- hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was present in the amount of

6%.

Finally, nitrilotris(methylenephosphonic acid) (NTMPA) was dissolved and mixed with the PC blend to obtain a fourth aqueous composition wherein the PC blend was present in the amount of 37% and the nitrilotris(methylenephosphonic acid) present in the amount of 6%.

Highly flowable concrete mixes, made by combining another Portland cement, OPC-C, with coarse and fine aggregates in proportions typical of a high flow Ready-mixed concrete mix design and containing 430 kg/m³ cement, were then prepared containing each of the four aqueous compositions described above. The workability of each of the four concrete samples was tested using a standard slump-flow cone test at intervals of 30 minutes over a period of two hours or until the concrete reached an unusable consistency. The data results, summarized in Table 5, indicate the preferred enhanced slump retention provided by the phosphonate additives, HEDPA and NTMPA, up to 90 minutes versus STPP and SG.

Table 5

^* Based on the ease of movement upon and cohesive non-segregating behaviour of the concrete

Example 6

The dispersing properties of the PC1/PC2 blend were also evaluated in formulations with SG, HEDPA, and NTMPA at lower blend ratios of the PC component to slump retaining additives in two different cement compositions,

OPC-C and a 50/50 blend of OPC-C and granulated blast furnace slag

(SLAG).

The control admixture was based on the PC1/PC2 blend with SG plus a defoamer. The amount of PC1/PC2 was 12.5% and SG was 4% by weight of solution.

Sodium tripolyphosphate (STPP) was dissolved and mixed with the same PC composition as above to obtain a second aqueous composition wherein the PC blend was present in the amount of 12.5% and the STPP was present in the amount of 4%. 1-hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was dissolved and mixed with the same PC composition as above to obtain a third aqueous composition wherein the PC was present in the amount of 12.5% and the 1- hydroxyethane-1 ,1-diphosphonic acid (HEDPA) was present in the amount of 4%.

Finally, NTMPA was dissolved and mixed with PC1/PC2 to obtain a fourth aqueous composition wherein the PC blend was present in the amount of 12.5% and the NTMPA in the amount of 4%.

Concrete mixes, made by combining OPC-C and coarse and fine aggregates in proportions typical of a high flow Ready-mixed concrete mix design and containing 430 kg/m³ cementitious content, were then prepared containing each of the four aqueous compositions described above. The workability of each of the four concrete samples was tested using a standard slump cone test at intervals of 30 minutes over a period of one hour or until the concrete reached an unusable consistency.

The data for the concrete mixes prepared with OPC-C and OPC/SLAG, are summarized in Tables 6a and 6b, respectively. The PC1PC2-HEDPA blend demonstrates consistent slump retention over 60 minutes when used with the two cementitious compositions, where as the PC1/PC2 blend with STPP appears less effective with the OPC/SLAG concrete mixture.

Table 6a

Strength

Table 6b

Example 7

The dispersing properties of a tertiary blend of polycarboxylate-type dispersants, identified as PC1/PC2/PC3 were evaluated in formulations containing SG and HEDPA using a white OPC identified as OPC-W.

The control was based on a blend of PC1/PC2/PC3 plus a defoamer. The amount of polymer blend was 28% by weight of solution. SG was dissolved and mixed with the same PC composition as above to obtain a second aqueous composition wherein the PC was present in the amount of 28% and SG was present in the amount of 3.5%.

Finally, HEDPA was dissolved and mixed with the same PC composition as above to obtain a third aqueous composition wherein the PC was present in the amount of 28% and HEDPA was present in the amount of 3.5%.

Concrete mixes, made by combining OPC-W, limestone powder and coarse and fine aggregates in proportions typical of a high flow Ready-mixed concrete mix design and containing 330/120 kg/m³ cement/limestone content, were then prepared containing each of the three aqueous compositions described above. The workability of each of the four concrete samples was tested using a standard slump cone test at intervals of 30 minutes over a period of two hours or until the concrete reached an unusable consistency.

The data results are summarized in Table 7 below.

Table 7

The concrete mixture without any slump retention-enhancing agent loses considerable workability by 90 minutes, while slump loss with SG is moderate. However, slump loss with the PC blend with HEDPA is minimal, and the 1-day compressive strengths comparable to the control mixture. Example 8

The dispersing properties of a tertiary blend of polycarboxylate-type dispersants, identified as PC5/PC3/PC4, were evaluated in formulations containing SG, HEDPA, and NTMPA using a self-consolidating mix design with a cementitious composition consisting of 50/50 OPC-B/SLAG blend. A control mix was based on the tertiary blend of PC5/PC3/PC4, SG, and a defoamer. The amount of PC blend was 20% and the amount of SG was 3.3% by weight of solution.

HEDPA was dissolved and mixed with the same PC/SG composition as above to obtain a second aqueous composition wherein the PC blend was present in the amount of 20%, SG at 3.3%, and HEDPA at 3.3%.

Finally, NTMPA was dissolved and mixed with the same PC/SG composition as above to obtain a third aqueous composition wherein the PC blend was present in the amount of 20%, SG at 3.3%, and NTMPA at3.3%

Self-compacting concrete (SCC) mixes, made by combining OPC-B with Slag in the proportion 250/200 kg/m³ respectively, and coarse and fine aggregates in proportions typical of a Ready-mixed SCC mix design, were then prepared containing each of the two aqueous compositions described above. The workability of each of the concrete samples was tested using a standard slump-flow cone test at intervals of 30 minutes over a period of two hours or until the concrete reached an unusable consistency. The data results, summarized in Table 8, indicate that the phosphonate additives can provide excellent slump-flow retention up to two hours. Excellent concrete rheology of the SCC mixtures containing the phosphonate additives was noted as the concrete appeared highly cohesive, and easy to move and non- segregating when mixed. Table 8

The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Skilled artisans can make variations and changes without departing from the spirit of the invention.

Claims

Claims:

1. A cement dispersing composition comprising:

(A) at least one cement dispersant comprising (i) sulphonated melamine formaldehyde condensate; (ii) sulphonated naphthalene formaldehyde condensate; or (iii) copolymers formed by polymerizing an acrylic or methacrylic monomer, a carboxylic acid monomer, and optional further monomer or monomers copolymerizable with the foregoing monomers; and

(B) a slump retention-enhancing agent that is 1-hydroxyethane-1,1- diphosphonic acid, or a salt thereof, wherein said slump retention-enhancing agent is chemically unreacted with said at least one cement dispersant, such that, when said cement dispersing composition is mixed with a hydratable cementitious mixture, said slump retention-enhancing agent molecules can move independently of the cement dispersant molecules with respect to the cement particles; and wherein said at least one cement dispersant is present in the amount of 2% - 50%, and wherein said slump retention-enhancing agent is present in the amount of 0.3% - 10%, all percentages herein are dry weight based on total weight of said cement dispersing composition.

2. The cement dispersing composition of claim 1 wherein said at least one cement dispersant comprises said copolymers, said copolymers comprising polyacrylate comb polymers.

3. The cement dispersing composition of claim 1 wherein said at least one cement dispersant comprises sulphonated naphthalene or melamine formaldehyde condensate.

4. The cement dispersing composition of any one of claims 1 to 3 further comprising a lignosulfonic acid or salt as an additional cement dispersant.

5. A cement composition comprising a cement binder and the cement dispersing composition of any one of claims 1 to 4.

6. A method for enhancing slump retention in a cementitious mixture, comprising mixing together (A) a cement binder; (B) at least one cement dispersant as defined in any one of claims 1 to 5; and (C) a slump retention- enhancing agent that is 1-hydroxyethane-1 ,1-diphosphonic acid, or a salt thereof, wherein said slump retention-enhancing agent is chemically unreacted with said at least one cement dispersant, such that, when said cement dispersing composition is mixed with a hydratable cementitious mixture, slump retention-enhancing agent molecules can move independently of cement dispersant molecules with respect to cement particles.